The present invention relates to a glass plate having electrically charge-preventive film of conductive organic polymer, its making method, a solution for making the film, and its manufacturing method. In detail, it relates to an anti-static film formed using electroconductive organic polymer on the surface of the glass plate, particularly, an image display faceplate or a screen portion in a panel of a CRT 1 so as to improve the electrically charge-preventive so anti-static characteristics of the glass plate, such as the image display faceplate.
Recently, a wide use of an anti-explosion type cathode ray tube allows a face cover glass to be unnecessary in a television receiver, a monitor, etc., regarding the prevention of electrostatic charge, thereby exposing the front portion of the cathode ray tube, and giving electric shock by charged electrical high voltage, to the person who comes access, to the faceplate of the cathode ray tube. Furthermore, dust in air, particles, etc., are adhered to by the electric force, and accumulated on, the charged faceplate of the cathode ray tube, thereby having the image on the display faceplate difficult to see.
The cause of electrostatic charge as to the faceplate panel as one example of the glass plate is as follows.
A thin and uniform aluminium film is deposited by vacuum on the phosphor screen structure on the interior surface of the faceplate panel. When a electric power is applied to, a high anode voltage is applied to the aluminium film. Electric charges generate on the exterior surface wall of the panel by electrostatic induction due to the high voltage of the inside aluminium film.
Korean patent publication No. 2713 as one prior arts for providing an anti-static characteristics on the image display faceplate describes one such anti-static coating formed by the steps of preparing a slurry by mixing an alcohol solution containing alkoxysilane Si(OR)4 (R is an alkyl group) and at least one of tin oxide, indium oxide and antimony oxide, spraying the slurry on the faceplate panel, and heat-treating the sprayed panel at a relatively low temperature.
U.S. Pat. No. 5,750,054, issued to Patrizia Cinquina, Vasto, et al. on May 12, 1998, discloses an anti-static, anti-glare coating for a reflective-transmissive surface wherein the surface is applied onto with a coating solution comprising a thiophene-based, electroconductive polymer and a siliceous material. As the concrete electroconductive polymer, polyethylenedioxythiophene, and as a siliceous material, lithium-stabilized silica sol and tetraethoxysilane are disclosed.
Further, U.S. Pat. No. 5,742,119 issued to Aben, et al. on Apr. 21, 1998, discloses a display screen of a cathode ray tube provided with an electroconductive coating of poly-3,4-ethylenedioxythiophene. The coating layer has a sheet resistance of 1 kilo-ohm/quadrature and a high transmission. The layer provides an effective shield against electromagnetic radiation. The coating can be provided with additional layers of, for example, silicon dioxide to improve the mechanical properties.
However, the metallic oxide costs too much, thereby making the manufacturing cost very high.
Further, the problem is that while the metallic oxide exists dispersedly in the alcohol solution, deposition problem arises due to cohesion between the particles according the condition of the surroundings, thereby making spots or unevenness and lowering the electroconductivity.
Accordingly, it is one object of the present invention to provide a glass plate such as image display faceplate having high-electroconductive film which can be formed using electroconductive organic polymer in a simple method and at a low cost, and have an improved anti-static characteristic with a strong film hardness and a strong adhesive strength. Also, the present invention provides a method of making such film , said method comprising the steps of obtaining a anti-static layer by dissolving in alcohol an aqueous solution of electroconductive organic polymers and applying the resultant dissolved solution, and then spin overcoating an alcoholic solution of silicon alkoxide and heat-treating the resultant overcoated film. If necessary, an additional anti-glare layer may be further formed by spraying the alcoholic solution of silicon alkoxide onto the anti-static layer or the resultant film of the alcoholic solution of silicon alkoxide.
To accomplish the aforementioned purpose, the present invention provides a glass plate on which an anti-static film is formed on the exterior surface, said film comprising a first coating layer formed containing an electroconductive organic polymeric component and a second coating layer of silica coating formed by being overcoated onto the first coating layer.
Said first coating layer may be formed by coating an electroconductive organic polymeric solution containing 0.005-0.5 wt. % of polyethylenedioxythiophene which polystyrenesulphonate is doped to and silicon alkoxide of below 10 wt. %, and said electroconductive organic polymeric solution may contain 40-90 wt. % of at least one alcoholic solvent selected from a group consisting of a methanol, an ethanol, an isopropanol, a butanol, and combinations thereof, 5-70 wt. % of pure water, and 1-20 wt. % of at least one co-solvent selected from a group consisting of a compound having a carbonyl group, an ether, and combinations thereof. And, said second coating layer is formed by overcoating with alkoxysilane Si(OR)4.
The anti-static film may have an anti-glare characteristic itself, and otherwise at least one anti-glare film formed thereon. Such glass plate may be an image display faceplate or a screen portion in a panel of a CRT.
Also, the present invention provides a method of forming a anti-static film on a surface of a glass plate, the method comprising the steps of: first-coating an electroconductive organic polymeric solution on the surface of the glass plate, said solution containing 0.005-0.5 wt. % of polyethylenedioxythiophene which polystyrenesulphonate is doped to and silicon alkoxide of below 10 wt. %; and second-coating alkoxysilane Si(OR)4 after the first-coating step.
Furthermore, the present invention provides a solution for applying onto a surface of a glass plate in order to form an anti-static film, said solution containing 0.005-0.5 wt. % of polyethylenedioxythiophene which polystyrenesulphonate is doped to, silicon alkoxide of below 10 wt. %, 40-90 wt. % of at least one alcoholic solvent selected from a group consisting of a methanol, an ethanol, an isopropanol, a butanol, and combinations thereof, 5-70 wt. % of pure water, and 1-20 wt. % of at least one co-solvent selected from a group consisting of a compound having a carbonyl group, an ether, and combinations thereof.
It is preferred, in the electroconductivity, that said solution contain said silicon alkoxide of below 2 wt. %.
Furthermore, the present invention provides a method of making a solution for applying onto a surface of a glass plate in order to form an anti-static film, said solution being prepared by the steps of: dissolving in alcohol an aqueous solution of electroconductive organic polymers; first-adding silicon alkoxide to the alcoholic solution for improving the cohesive strength; and second-adding pure water and an inorganic acid catalyst for hydrolysis, and co-solvent for improving the application property.
The anti-static film formed by such method, comprises a first coating layer having fine porosities and an excellent electroconductive property, and a second coating layer formed by being overcoated with a material of a strong adhesive strength onto the first coating layer so as to adhere to at least the glass plate by penetrating through the porosities of the first coating layer, thus the anti-static film is adhered to the glass plate due to the strong adhesive strength without being scaled off and with obtaining an excellent electroconductive characteristic of the first coating layer.